2_Computer Science Grade 10 Principles of textual programming Presentation

10.2.3.1 compare tables for character encoding such as Unicode and ASCII

COMPUTER SCIENCE

NIS, Aktau

Learning Objectives/Assessment criteria

Encode text with ASCII and Unicode

ASCII

Computers have to be able to represent letters and symbols as well as numbers. Simply, the idea is to give each character a number, as a code and store the codes and their meanings in a table.

A common code is ASCII - the American Standard Code for Information Interchange.

This uses seven bits to store characters. Seven bits is enough to code 128 different characters.

Using this information write a definition of ASCII in your exercise books. You do need to know what it stands for and how many bits it uses.

Activity 1

Activity 2

Use the table of ASCII binary codes to decode this:

Activity 3

Copy and complete the questions below.

Unicode

Unicode is an alternative character set and encoding system. It uses 16 bits to encode each character and is therefore able to represent far more characters than ASCII (over 65,000).

Write this definition of Unicode in your exercise books.

Bitmap Images

Images can be represented using a grid of squares called pixels. Each pixel can be uniquely identified by its position in the grid (x/y coordinates) and each pixel is a single colour.

Write this definition of a Bitmap Image in your exercise book.

http://learncomputing.org/bitmap.php

Colour Depth

A binary code is used to represent the colour of a pixel. The number of bits used to store each pixel’s colour is known as the colour depth. The greater the colour depth, the more colours can be represented.

The number of colours that can be represented can be calculated using 2depth. For example a colour depth of 1 bit can represent 2 colours.

2no. of bits

Therefore 3 bits = 23

Write this definition of Colour Depth in your exercise book.

Activity 4

Copy and complete the colour depth table below.

1-Bit Images

This image has only two colours, black and white and therefore has a colour depth of 1 bit.

1, 0, 0, 0, 1

1, 1, 1, 1, 0

1, 0, 0, 0, 0

0, 1, 1, 1, 0

0, 1, 1, 1, 0

1, 0, 0, 0, 0

Activity 5

Copy and complete the grid below to reveal what character this code produces.

Use a ruler.

Activity 6

Produce the binary code to produce the letter ‘G’ in the grid below.

Use a ruler.

How could his be stored more efficiently?

This image has only two colours, black and white.

1, 3, 1

4, 1

1, 4

0, 1, 3, 1

0, 1, 3, 1

1, 4

Complete the Image Representation worksheet using this method.

Resolution and File Size

The resolution or pixel density of an image is the number of pixels per inch (PPI). Generally speaking the higher the resolution the higher the quality of the image.

You can calculate the amount of storage space required to save an image using a formula.

Calculate the file size of an image with
- dimensions of 2 inches x 3 inches- resolution (also called pixel density) of 200 PPI - colour depth of 4 bits.

(2 * 200) * (3*200) * 4 / 8

Activity 7

Calculate the file size of an image with dimensions of 3 inches x 4 inches, a pixel density (also known as resolution) of 300 pixels per inch and a colour depth of 8 bits. Give your answer in bytes.

(3 * 300) * (4*300) * 8 / 8

Activity 8

Calculate the file size of an image with dimensions of 5 inches x 7 inches, a pixel density of 400 pixels per inch and a colour depth of 3 bits. Give your answer in bytes.

(5 * 400) * (7*400) * 3 / 8